I was going to post something similar. You're right, the system was essentially an oligarchy and there is no way to expect all (or even most) citizens of voting age to possess those traits, especially given human nature, the depravity of which was recognized by the Framers.
That being said, I still think we probably have the best system we could hope for. Look at the hysteria surrounding Obama's election and then imagine what it would have looked like if Obama had been elected Prime Minister in a system similar to that of the United Kingdom, where the meat of Obama's agenda had been passed long ago.
A parliamentary system is much more responsive to the whims, passions, and prejudices of the people, and that is not necessarily a good thing. Imagine what Prime Minister Bush and Lord Cheney could have passed through following 9/11 had we been in a parliamentary system.